The effect of microglia activation on cerebral injury induced by conditional Tpk knockout in brain neurons of adult mice and the mechanism exploration

Abstract

AbstractBackgroundWe previously designed and constructed the neuronal Tpk conditional knockout mouse model, which can simulate various pathophysiological changes of Alzheimer’s disease (AD). The objective of this study was to explore the effect and mechanism of microglia activation induced by the conditioned neuronal Tpk knockout on neuronal injury.MethodWe selected the 3‐month‐old CaMKII‐CreERT2/+ ; Tpkfl/fl (Tpk‐cKO) and negative control mice Tpkfl/f (Control) from the same nest. The mice were given CSF1R inhibitor (PLX3397)respectively during the whole stage (the 2nd∼10th weeks after induction), the late stage (the 6th∼10th weeks after induction), and the early stage (the 2nd∼6th weeks after induction) to eliminate microglia during whole/early/late stage. Besides, the single‐cell RNA sequencing (scRNA‐seq) analysis was performed at different time courses.ResultAccording to scRNA‐seq analysis, Microglia can be divided into different subgroups, which have different functions and proportions, and their pseudotime states were quite distinct. Among them, microglia subgroup 5 was highly distributed in the early pseudotime state playing the role of immune regulation and neuroprotection, while subgroup 6 was mainly distributed in the late pseudotime state contributing to phagocytosis damage. Therefore, when microglia were eliminated for the whole period, the protective effect of microglia was completely lost leading to more cerebral injury. Eliminating microglia at the early stage, the cerebral injury was alleviated because the repopulated microglia was still in the early pseudotime state performing immunomodulatory and neuroprotective functions. Eliminating microglia at late stage can also mitigate the cerebral injury, mainly because it not only has received the immunomodulatory and neuroprotective effects in the early stage, but also reduce the phagocytic damage in the late stage.ConclusionThe overall effect and mechanism of microglia activation induced by neuronal Tpk conditional knockout on cerebral injury are distinct in different stages, which is associated with the function and proportion of microglia clusters. The major effect of microglia at the early stage was immunoregulation and neuroprotection induced by cluster 5, and the general effect of the late stage was phagocytic damage mainly provided by cluster 6.